The present invention relates generally to the field of non-destructive testing of components and in particular to a new and useful method and apparatus for the non-destructive inspection of boiler tubes for cracks using electromagnetic acoustic transducer technology.
Various nondestructive methods such as ultrasonic (UT), eddy current (ET), magnetic particle (MT), and dye penetrant (PT), have been used for the detection of cracks in boiler tubes. All have serious limitations that prevent their use for real time, high speed inspection of boilers for surface breaking cracks. UT requires a liquid couplant which can produce extraneous signals. EC is very susceptible to material properties/variations inherent within a material which can produce signals that mask the defect signals or can be mistakenly interpreted as defects. Both MT and PT require large amounts of chemicals and are not suited for high speed inspection of boilers due to the time required for chemical application and signal interpretation, plus disposal of used chemicals.
Electromagnetic acoustic transducers (here EMATs or emats) are known for use in testing materials for defects. In known systems, a signal generator creates an acoustic wave which propagates through a test material and either the original signal or a reflection is received by a single sensor having a coil for converting acoustic wave energy to an electrical current. EMATs are typically used on planar surfaces of a test material to detect both surface and sub-surface defects in the test material.
Tubes present a challenge for testing due to their curved surfaces. Tubes used in industrial boilers present a further challenge, as the space around and access to the tubes is typically very limited. These tubes must be as free of defects as possible, and coated with materials to resist corrosion and breakdown in the harsh environment of an industrial boiler.